Antenna device and wireless communication device

ABSTRACT

An antenna device includes a feed coil and a sheet conductor. The feed coil includes a magnetic core and a coil-shaped conductor, which is provided around the magnetic core. An RFIC is connected to the feed coil. The sheet conductor has a larger area than the feed coil. A slit that extends from a portion of the edge of the sheet conductor toward the inner side of the sheet conductor is provided in the sheet conductor. The feed coil is arranged such that the direction of the axis around which the feed coil is disposed is parallel or substantially parallel to the directions in which the sheet conductor extends. The feed coil is arranged such that the feed coil is close to the slit and one of coil openings at the ends of the feed coil faces the slit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an antenna device preferably for use ina radio frequency identification (RFID) system or in a near fieldwireless communication system and to a wireless communication devicethat includes such an antenna device.

2. Description of the Related Art

Generally, for RFID in the 13.56 MHz band such as near fieldcommunication (NFC) used for mobile terminals, an RFID chip and amatching device are mounted on a circuit board, an antenna is attachedto the inner side of a terminal housing made of resin, and the RFID chipand an antenna are connected via a spring pin or the like in a directcurrent (DC) manner.

Recent wireless communication devices such as mobile phone terminalshave become thinner. In order to cope with insufficient strength due tosuch thinning, it is increasingly the case that strength is improved byusing “more metal” when a housing is made. For example, a resin housingis coated with magnesium or a metal housing made of a material, such asaluminum or carbon fiber, is used.

However, when more metal” is used to make a housing, an antenna builtinto a terminal is shielded by the metal. Thus, a problem arises in thatcommunication may not be able to be performed with another device.

As a result, antenna devices have been proposed in Japanese UnexaminedPatent Application Publication No. 2011-97657 and Japanese UnexaminedPatent Application Publication No. 2011-249935. The antenna devices havea structure in which a metal plate, which has a larger area than anantenna coil, is used as a radiation plate by being arranged to be closeto the antenna coil (magnetic-field coupling).

However, the antenna devices described in Japanese Unexamined PatentApplication Publication No. 2011-97657 and Japanese Unexamined PatentApplication Publication No. 2011-249935 have the following problems.

FIG. 25 is a plan view of an antenna device described in JapaneseUnexamined Patent Application Publication No. 2011-97657. A conductoropening CA and a slit 2S are provided in a sheet conductor 2. A coilopening of a coil-shaped conductor 31 is arranged so as to overlap theconductor opening CA. When current flows in the coil-shaped conductor 31in the directions indicated by arrows drawn with a solid line, a currentthat flows in the sheet conductor 2 in the directions indicated byarrows drawn with a broken line is induced. In FIG. 25, the current thatflows in the coil-shaped conductor 31 and the current that flows in thesheet conductor 2 flow in the same direction in areas A1, A2, A3, andA4. However, the current that flows in the coil-shaped conductor 31 andthe current that flows in the sheet conductor 2 flow in oppositedirections in an area B. In this manner, when there is an area in whichthe directions of currents are opposite, the inductance of an antenna (acapacitor) is reduced and communication characteristics are degraded,which is a problem. Moreover, the amount of induced current changes inaccordance with positions in which the coil-shaped conductor 31 and thesheet conductor 2 are attached and variations in distance between thecoil-shaped conductor 31 and the sheet conductor 2 when they areattached. Thus, variations in inductance tend to occur, which is aproblem.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide an antenna devicethat overcomes the problems described above, such as a reduction ininductance of an antenna device when viewed from a feeder circuit andvariations in inductance and a wireless communication device thatincludes such an antenna device.

An antenna device according to a first preferred embodiment of thepresent invention includes a feed coil that includes a coil-shapedconductor, and a sheet conductor, which preferably has a sheet shape.The sheet conductor preferably has a larger area than the feed coil. Aslit that extends from a portion of the edge of the sheet conductortowards an inner side of the sheet conductor is provided in the sheetconductor or an opening and the slit are provided in the sheetconductor, the opening being connected to the slit. The feed coil isarranged such that the direction of the axis around which thecoil-shaped conductor is disposed differs from a direction perpendicularor substantially perpendicular to the sheet conductor. The feed coil isarranged such that a coil opening at one end of the coil-shapedconductor is close to the slit or a portion of the edge of the openingand the coil opening faces the slit or the portion of the edge of theopening.

An antenna device according to a second preferred embodiment of thepresent invention includes a feed coil that includes a coil-shapedconductor, and a sheet conductor. The sheet conductor includes aplurality of sheet conductors and a slit is provided or an opening andthe slit are provided between adjacent sheet conductors of the pluralityof sheet conductors, the opening being connected to the slit. The totalarea of the plurality of sheet conductors and slit is preferably largerthan the area of the feed coil. The feed coil is arranged such that thedirection of the axis around which the coil-shaped conductor is disposeddiffers from at least a direction perpendicular or substantiallyperpendicular to one of the plurality of sheet conductors, the sheetconductor being closest to the feed coil. The feed coil is arranged suchthat a coil opening at one end of the coil-shaped conductor is close tothe slit or a portion of the edge of the opening and the coil openingfaces the slit or the portion of the edge of the opening.

In the structures described in the first and second preferredembodiments, “close” refers to a range in which a communication distanceobtained by using the feed coil and the sheet conductor is greater thana communication distance obtained only by using the feed coil. With thisstructure, there is substantially no area in which the current thatflows in the feed coil and the current that flows in the sheet conductorflow in opposite directions. Thus, there are no problem, such as areduction in inductance of an antenna and a variation in inductance.

According to a third preferred embodiment of the present invention, theplurality of sheet conductors are preferably connected to each other ina direct current manner and are at the same potential. With thisstructure, the plurality of sheet conductors function as shieldconductors.

According to a fourth preferred embodiment of the present invention, theantenna device may preferably include a plurality of sheet conductorsthat include a first conductor surface and a second conductor surfacethat face each other, and may preferably include a first connection unitthat electrically and directly connects the first conductor surface withthe second conductor surface and a second connection unit that connectsthe first conductor surface with the second conductor surface via afirst capacitor. With this structure, coupling occurs between the feedcoil and the first conductor surface and a space between the firstconductor surface and the second conductor surface functions as anopening. Thus, the first and second conductor surfaces may be used asradiation elements without a slit or an opening being provided in aconductor surface.

According to a fifth preferred embodiment of the present invention, thefeed coil may preferably have a multilayer structure in which aplurality of insulator layers (for example, magnetic layers, dielectriclayers, or layers made by mixing a dielectric material and a magneticmaterial) on which a conductor that defines an inductor is provided anda plurality of insulator layers (for example, magnetic layers,dielectric layers, or layers made by mixing a dielectric material and amagnetic material) on which a conductor that defines a capacitor isprovided are stacked, and the first capacitor may be the capacitor thatthe feed coil includes. With this structure, a capacitor element is notrequired to connect the first and second conductor surfaces. Thus, acapacitor may be built into the antenna without increasing the sizethereof, and consequently, space savings on the circuit board isachieved.

According to a sixth preferred embodiment of the present invention, theslit may preferably include at least one bent portion. With thisstructure, a high degree of flexibility in the arrangement position andorientation of the feed coil with respect to the sheet conductor isprovided.

According to a seventh preferred embodiment of the present invention,the axis around which the coil-shaped conductor is disposed ispreferably arranged so as to be perpendicular or substantiallyperpendicular to the direction in which the slit extends or to a portionof the edge of the opening. With this structure, coupling mostefficiently occurs for the feed coil through a magnetic field generatedby a current that flows along the edge of the slit or opening.

According to an eighth preferred embodiment of the present invention,the sheet conductor preferably includes a resonant circuit that isprimarily defined by the slit or the edge of the opening. The resonantfrequency of the resonant circuit is preferably the same orsubstantially the same as the resonant frequency of a circuit thatincludes the feed coil. With this structure, the radiation efficiencydue to the sheet conductor is increased.

According to a ninth preferred embodiment of the present invention, atleast a portion of the sheet conductor is preferably defined by a metalhousing. With this structure, there is no need to provide a dedicatedcomponent as a sheet conductor. Thus, the number of components isreduced.

According to a tenth preferred embodiment of the present invention, atleast a portion of the sheet conductor is preferably defined by a groundconductor provided on a circuit board. With this structure, there is noneed to provide a dedicated component as a sheet conductor. Thus, thenumber of components is reduced.

A wireless communication device according to an eleventh preferredembodiment of the present invention includes the antenna deviceaccording to the first preferred embodiment of the present invention anda communication circuit connected to the antenna device.

A wireless communication device according to a twelfth preferredembodiment of the present invention includes the antenna deviceaccording to the second preferred embodiment of the present inventionand a communication circuit connected to the antenna device.

According to various preferred embodiments of the present invention, anantenna device that does not experience a reduction in inductance and/ora variation in inductance and a wireless communication device thatincludes the antenna device are provided. This is because there issubstantially no area in which the current that flows in the feed coiland the current that flows in the sheet conductor flow in oppositedirections.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an antenna device according to a firstpreferred embodiment of the present invention and an antenna coil withwhich the antenna device performs communication.

FIGS. 2A to 2C are diagrams illustrating relationships between a slitand a feed coil in terms of position, orientation, and couplingstrength.

FIG. 3 is a perspective view of an antenna device according to a secondpreferred embodiment of the present invention.

FIG. 4 is a perspective view of another antenna device according to thesecond preferred embodiment of the present invention.

FIGS. 5A to 5C are diagrams illustrating states of coupling between thefeed coil and a sheet conductor for another antenna device according tothe second preferred embodiment of the present invention.

FIGS. 6A and 6B are perspective views of antenna devices according to athird preferred embodiment of the present invention.

FIG. 7 is a perspective view of an antenna device according to a fourthpreferred embodiment of the present invention.

FIG. 8 is a diagram illustrating an inductor formation section of thesheet conductor of the antenna device according to the fourth preferredembodiment of the present invention.

FIG. 9 is a perspective view of another antenna device according to thefourth preferred embodiment of the present invention.

FIG. 10 is a perspective view of an antenna device according to a fifthpreferred embodiment of the present invention.

FIG. 11A is a perspective view of the sheet conductor included inanother antenna device according to the fifth preferred embodiment ofthe present invention.

FIG. 11B is a front view of the other antenna device.

FIGS. 12A and 12B are perspective views of antenna devices according toa sixth preferred embodiment of the present invention.

FIG. 13 is a plan view illustrating an internal structure of a wirelesscommunication device that includes an antenna device according to aseventh preferred embodiment of the present invention.

FIG. 14 is a perspective view of the feed coil, which is modularized,according to the seventh preferred embodiment of the present invention.

FIG. 15 includes a diagrams illustrating an internal structure of awireless communication device that includes an antenna device accordingto an eighth preferred embodiment of the present invention, the diagramsbeing plan views that separately show a state of the inside of an upperhousing and a state of the inside of a lower housing.

FIG. 16A is a perspective view of an antenna device according to a ninthpreferred embodiment of the present invention.

FIG. 16B is a front view of the antenna device.

FIG. 17 is a front view of an antenna device that illustrates anotherexample of a state in which the feed coil is arranged.

FIG. 18A is a perspective view of an antenna device according to a tenthpreferred embodiment of the present invention.

FIG. 18B is a front view of the antenna device.

FIG. 19 is a side view of the antenna device.

FIG. 20 is a perspective view of an antenna device according to aneleventh preferred embodiment of the present invention.

FIG. 21 is an exploded perspective view of a feed coil used in anantenna device according to a twelfth preferred embodiment of thepresent invention.

FIG. 22 is a diagram illustrating a part of a board on which a feed coilaccording to the twelfth preferred embodiment is mounted of the presentinvention.

FIG. 23 is an exploded perspective view of a feed coil of anotherexample.

FIG. 24 is an exploded perspective view of a feed coil of anotherexample.

FIG. 25 is a plan view of an antenna device described in JapaneseUnexamined Patent Application Publication No. 2011-97657.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First PreferredEmbodiment

FIG. 1 is a perspective view of an antenna device according to a firstpreferred embodiment of the present invention and an antenna coil withwhich the antenna device performs communication. The antenna deviceincludes a feed coil 3 and a sheet conductor 2. The feed coil 3 includesa magnetic core 32 and a coil-shaped conductor 31, which is arrangedaround the magnetic core 32. The coil-shaped conductor 31 may preferablybe a conducting wire (a wound conductor wire) wound around the magneticcore 32 or may be a conductor pattern provided in a multilayer bodyincluding a plurality of stacked dielectric layers, a multilayer bodyincluding a plurality of stacked magnetic layers, or a multilayer bodyincluding one or more dielectric layers and one or more magnetic layersthat are stacked on one another. In particular, the feed coil 3 ispreferably a chip-type feed coil that includes, as the coil-shapedconductor 31, a coil-shaped conductor including an in-plane conductorpattern and an interlayer conductor pattern in a multilayer bodyincluding a plurality of stacked magnetic layers (for example, ferriteceramic layers) since a chip-type feed coil, which is relatively smalland may be surface-mounted, may be provided.

A radio-frequency integrated circuit (RFIC) 13, which is a feedercircuit, is connected to the feed coil 3. That is, one end and the otherend of the coil-shaped conductor 31 are connected to two input-outputterminals of the RFIC 13. In the first preferred embodiment, the RFIC 13is preferably an RFIC chip for near field communication (NFC) and is asemiconductor IC chip that processes high-frequency signals for NFC, forexample.

The sheet conductor 2 preferably has a larger area than the feed coil 3.That is, when viewed in a direction perpendicular or substantiallyperpendicular to the sheet conductor 2, the sheet conductor 2 preferablyhas larger outer dimensions than the feed coil 3. The sheet conductor 2includes a slit 2S that extends from a portion of a side of the sheetconductor 2 towards the inner side of the sheet conductor 2. In thefirst preferred embodiment, the slit 2S preferably has a constant widthfrom one end to the other end thereof. However, the width does notnecessarily have to be constant.

In this example, the sheet conductor 2 is a metal housing portion (ametal cover portion) of a communication terminal housing. In a stateillustrated in FIG. 1, the feed coil 3 is arranged under the sheetconductor 2, in the communication terminal housing. The feed coil 3 isarranged such that the direction of the axis around which thecoil-shaped conductor 31 is disposed differs from a directionperpendicular or substantially perpendicular to the sheet conductor 2.More specifically, the feed coil 3 is arranged such that the directionof the axis around which the coil-shaped conductor 31 is disposed isparallel or substantially parallel to the directions in which the sheetconductor 2 extends. Note that the direction of the axis around whichthe coil-shaped conductor 31 is disposed does not have to be exactlyparallel to the directions in which the sheet conductor 2 extends. Theaxis around which the coil-shaped conductor 31 is disposed is preferably±45° or less with respect to the directions in which the sheet conductor2 extends.

Moreover, the feed coil 3 is arranged such that one of coil openings atthe ends of the feed coil 3 is close to the slit 2S and faces the slit2S (the “coil openings at the ends of the feed coil 3” are hereinaftersimply referred to as “coil openings of the feed coil 3”). That is, thefeed coil 3 is arranged such that the magnetic flux that passes throughthe slit 2S of the sheet conductor 2 passes through the coil opening,that is, the feed coil 3 is arranged such that the coil opening may beseen from the slit 2S.

The sheet conductor 2 does not necessarily have to be a metal housingportion and may be a conductive film provided on an insulating base or aconductor layer provided in an insulating base. That is, the sheetconductor 2 may preferably be a ground conductor mounted in acommunication terminal, various types of metal plate, such as a metalchassis, a shield case, or a metal cover of a battery pack, or a flatpattern of a metal thin film provided on a flexible sheet, for example.In the case in which the sheet conductor 2 is a metal thin film patternprovided on a flexible sheet, the sheet conductor 2 is preferablyattached to the inner side of the back cover of a communication terminalby using an adhesive, for example. Note that the sheet conductor 2 ispreferably a conductor that is substantially sheet-shaped, and the sheetconductor 2 does not have to be flat, and may be curved.

As illustrated in FIG. 1, an RFIC 14 is connected to an antenna coil 4,with which communication is performed. When the sheet conductor 2 isclose to the antenna coil 4, an induced current is generated in thesheet conductor 2 and flows primarily along the edge of the sheetconductor 2 due to the cut-edge effect. That is, current (an eddycurrent) flows in a direction such that the current flowing in thatdirection prevents magnetic flux generated by the antenna coil 4 frompassing through the antenna coil 4. In FIG. 1, magnetic flux that passesthrough the antenna coil 4 is denoted by φ1. The slit 2S is defined by aportion of the edge of the sheet conductor 2, and a current density ishigh in a portion along the edge of the slit 2S. As the width of theslit 2S is decreased, the magnetic force near the slit 2S increases. InFIG. 1, magnetic flux that passes through the slit 2S is denoted by φ2.A portion of the magnetic flux φ2 enters the feed coil 3. Note that amagnetic field is also generated by a current that flows along the edgeportion of the periphery of the sheet conductor 2. However, strongcoupling occurs for the feed coil 3 primarily through a magnetic fieldnear the slit 2S since the feed coil 3 is sufficiently spaced apart fromthe edge portion of the periphery of the sheet conductor 2. Themagnetic-field coupling described above is not cancelled bymagnetic-field coupling occurring through a magnetic field near the endportion of the periphery of the sheet conductor 2.

As described above, the sheet conductor 2 functions as a magnetic-fieldcapturing element (a radiation plate) and magnetic-field coupling occursbetween the feed coil 3 and the antenna coil 4, with which communicationis performed, via the sheet conductor 2. Moreover, the coil openings ofthe coil-shaped conductor 31 of the feed coil 3 do not face the sheetconductor 2 and only a portion of the coil-shaped conductor 31 is closeto the sheet conductor 2. Furthermore, when viewed in the direction ofthe axis around which the coil-shaped conductor 31 is disposed, thecoil-shaped conductor 31 includes a portion near the sheet conductor 2and a portion spaced away from the sheet conductor 2. Thus, theinductance of the feed coil 3 does not significantly change even when apositional relationship between the feed coil 3 and the sheet conductor2 changes to a certain degree. Therefore, the antenna devices may havesmall manufacturing variations.

The feed coil 3 is preferably arranged such that one of the coilopenings of the feed coil 3 faces the slit 2S. As illustrated in FIG. 1,the direction of the axis around which the coil-shaped conductor 31 ofthe feed coil 3 is disposed (hereinafter also referred to as the axis ofthe feed coil 3) is preferably perpendicular or substantiallyperpendicular to the direction in which the slit 2S extends (that is, tothe direction of the longer side of the slit 2S), and coupling occurswith a high degree of efficiency for the feed coil 3 through themagnetic flux φ2 generated at the slit 2S.

FIGS. 2A to 2C are diagrams illustrating relationships between the slit2S and the feed coil 3 in terms of position, orientation, and couplingstrength. In FIGS. 2A to 2C, double-headed arrows drawn with a solidline represent the axis of the feed coil 3. In FIGS. 2A and 2C,double-headed arrows drawn with a broken line represent the direction inwhich the slit 2S extends. In FIG. 2B, a double-headed arrow drawn witha broken line represents the width direction of the slit 2S (or thedirection of the shorter side of the slit 2S).

Similarly to the first preferred embodiment illustrated in FIG. 1, FIG.2A illustrates an example in which the feed coil 3 is arranged such thatone of the coil openings of the feed coil 3 faces the slit 2S and thedirection of the axis of the feed coil 3 is perpendicular orsubstantially perpendicular to the direction in which the slit 2Sextends. With this structure, strong coupling between the feed coil 3and the sheet conductor 2 occurs through the magnetic field generated atthe slit 2S.

FIG. 2B illustrates an example in which the feed coil 3 is arranged suchthat one of the coil openings of the feed coil 3 faces a closed end,which is in the sheet conductor 2, of the slit 2S and the direction ofthe axis of the feed coil 3 is perpendicular or substantiallyperpendicular to the width direction of the slit 2S. With thisstructure, coupling occurs for the feed coil 3 through the magneticfield generated by a current that flows along the closed end of the slit2S. Thus, although coupling strength is weak, coupling between the feedcoil 3 and the sheet conductor 2 occurs.

FIG. 2C illustrates an example in which the feed coil 3 is arranged suchthat the coil openings of the feed coil 3 face both sides of the sheetconductor 2 with respect to the slit 2S and the direction of the axis ofthe feed coil 3 is perpendicular or substantially perpendicular to thedirection in which the slit 2S extends. With this structure, for thefeed coil 3, coupling occurs through a magnetic field generated bycurrent that flows along one side of the slit 2S and through a magneticfield generated by current that flows along another side of the slit 2S,the one side and the other side of the slit 2S facing each other. Thedirection of the magnetic field generated at the one side of the slit 2Sis opposite to the direction of the magnetic field generated at theother side of the slit 2S. Thus, for the feed coil 3, coupling throughthe magnetic field at the one side of the slit 2S and coupling throughthe magnetic field at the other side of the slit 2S balance each otherout. Therefore, coupling does not occur between the feed coil 3 and thesheet conductor 2.

Thus, the feed coil 3 is preferably arranged such that one of the coilopenings of the feed coil 3 faces the slit 2S and the direction of theaxis of the feed coil 3 is perpendicular or substantially perpendicularto the direction in which the slit 2S extends.

Second Preferred Embodiment

FIG. 3 is a perspective view of an antenna device according to a secondpreferred embodiment of the present invention. In this example, a slitprovided in the sheet conductor 2 includes slit portions 2Sa and 2Sb,the direction in which the slit portion 2Sa extends being perpendicularor substantially perpendicular to the direction in which the slitportion 2Sb extends. That is, the slit includes a bent portion. A feedcoil 3 a is preferably arranged such that one of coil openings of thefeed coil 3 a faces the slit portion 2Sa and the direction of the axisaround which the feed coil 3 a is disposed is perpendicular orsubstantially perpendicular to the direction in which the slit portion2Sa extends. Thus, strong coupling occurs for the feed coil 3 a througha magnetic field generated at the slit portion 2Sa. Moreover, a feedcoil 3 b is preferably arranged such that one of coil openings of thefeed coil 3 b faces the slit portion 2Sb and the direction of the axisaround which the feed coil 3 b is disposed is perpendicular orsubstantially perpendicular to the direction in which the slit portion2Sb extends. Thus, strong coupling occurs for the feed coil 3 b througha magnetic field generated at the slit portion 2Sb.

In this example, two feed coils 3 a and 3 b are preferably provided.However, only one of the feed coils 3 a and 3 b may also be provided.Moreover, these two feed coils 3 a and 3 b may be connected in series orin parallel. Additionally, three or more feed coils may be provided.

FIG. 4 is a perspective view of another antenna device according to thesecond preferred embodiment. In this example, the slit 2S and an opening2A are provided in the sheet conductor 2. The feed coil 3 is arrangedsuch that the feed coil 3 is close to the opening 2A and one of the coilopenings of the feed coil 3 faces the opening 2A. Thus, strong couplingoccurs for the feed coil 3 through a magnetic field generated at theedge of the opening 2A. Note that the feed coil 3 is not affected by theslit 2S since the direction of the axis of the feed coil 3 isperpendicular or substantially perpendicular to the direction of amagnetic field generated near the slit 2S. Moreover, a magnetic field isgenerated by a current that flows along the edge portion of theperiphery of the sheet conductor 2. However, strong coupling occurs forthe feed coil 3 primarily through a magnetic field near the opening 2Asince the feed coil 3 is provided closer to the opening 2A than to theedge portion of the periphery of the sheet conductor 2. Themagnetic-field coupling described above is not cancelled bymagnetic-field coupling occurring through a magnetic field near the endportion of the periphery of the sheet conductor 2.

FIGS. 5A to 5C are diagrams illustrating states of coupling between thefeed coil 3 and the sheet conductor 2 for another antenna deviceaccording to the second preferred embodiment. The slit 2S and theopening 2A are provided in the sheet conductor 2 of this antenna device,the width of the slit 2S being different from that of the opening 2A. InFIGS. 5A to 5C, double-headed arrows drawn with a solid line representthe axis of the feed coil 3. In FIGS. 5A and 5C, double-headed arrowsdrawn with a broken line represent the direction in which the slit 2Sextends. In FIG. 5B, a double-headed arc-shaped arrow drawn with abroken line represents the direction of a current that flows along theopening 2A.

In an example illustrated in FIG. 5A, strong coupling occurs for thefeed coil 3 through a magnetic field generated near the slit 2S. In anexample illustrated in FIG. 5B, strong coupling occurs for the feed coil3 through a magnetic field near the feed coil 3 from among a magneticfield generated near the opening 2A. In an example illustrated in FIG.5C, for the feed coil 3, coupling through a magnetic field at one sideof the slit 2S and coupling through a magnetic field at another side ofthe slit 2S balance each other out, the magnetic fields being generatedby a current that flows along the edge of the slit 2S. This is becausethe direction of the magnetic field at the one side of the slit 2S isopposite to the direction of the magnetic field at the other side of theslit 2S, the one side and the other side of the slit 2S facing eachother. Moreover, the direction of the axis of the feed coil 3 isperpendicular or substantially perpendicular to the direction of themagnetic field near the feed coil 3 from among the magnetic fieldgenerated near the opening 2A, and consequently, coupling does not occurbetween the feed coil 3 and the sheet conductor 2.

Note that the opening 2A illustrated in FIGS. 4 to 5C may be consideredas a wide portion of the slit 2S, the wide portion being wider than theremainder of the slit 2S. With this structure, in the case in which alens unit of a camera module is provided in the opening 2A or in thewide portion of the slit 2S, the sheet conductor 2 may be provided in anarea that includes the camera module. The opening 2A may be used as ahole in which not only a lens unit of a camera module but also variousfunctional units, such as a speaker or a microphone, for example, may beprovided.

Third Preferred Embodiment

FIGS. 6A and 6B are perspective views of antenna devices according to athird preferred embodiment of the present invention. Both of FIGS. 6Aand 6B illustrate examples in which two sheet conductors 2 a and 2 b areprovided. In addition, the slit 2S is provided between the sheetconductors 2 a and 2 b. The total area of the sheet conductors 2 a and 2b and slit 2S is preferably larger than the area of the feed coil 3.That is, when viewed in a direction perpendicular or substantiallyperpendicular to each of the sheet conductors 2 a and 2 b, the outerdimensions of the sheet conductors 2 a and 2 b are larger than those ofthe feed coil 3.

The feed coil 3 is preferably arranged such that the feed coil 3 isclose to the side on which the sheet conductor 2 a is provided and oneof the coil openings of the feed coil 3 faces the slit 2S and thedirection of the axis of the feed coil 3 is perpendicular orsubstantially perpendicular to the direction in which the slit 2Sextends. Thus, similarly to the antenna device illustrated in the firstpreferred embodiment, coupling occurs between the feed coil 3 and thesheet conductor 2 a. Coupling occurs between the sheet conductors 2 band 2 a via the slit 2S. As a result, the sheet conductors 2 a and 2 bfunction as magnetic-field capturing elements (radiation plates) andmagnetic-field coupling occurs between the feed coil 3 and the antennacoil 4, with which communication is performed, via the sheet conductors2 a and 2 b. In the third preferred embodiment, a main surface of thesheet conductor 2 a is preferably planar or substantially planar with amain surface of the sheet conductor 2 b and the feed coil 3 is arrangedsuch that the direction of the axis around which the coil-shapedconductor 31 is disposed is parallel or substantially parallel to thedirections in which each of the sheet conductors 2 a and 2 b extends.

In the above-described examples, two sheet conductors are preferablyprovided, for example. However, three or more sheet conductors may beprovided. Moreover, in the third preferred embodiment, the sheetconductors 2 a and 2 b are preferably electrically independent from eachother. However, they may be connected to each other.

Fourth Preferred Embodiment

FIG. 7 is a perspective view of an antenna device according to a fourthpreferred embodiment of the present invention. Different from theantenna device illustrated in FIG. 1 in the first preferred embodiment,a capacitor 5 is connected to the sheet conductor 2 near an open end ofthe slit 2S so as to straddle the slit 2S. An example of the capacitor 5is a chip capacitor.

FIG. 8 is a diagram illustrating an inductor formation section of thesheet conductor 2 of the antenna device according to the fourthpreferred embodiment. In the case in which the capacitor 5 is connectedto the sheet conductor 2 near the open end of the slit 2S so as tostraddle the slit 2S, an inductor whose inductance primarily correspondsto an electrical length of an edge 2SP (a broken line in FIG. 8) of theslit 2S is provided. An LC circuit, which is a resonant circuit, isdefined by the inductor and the capacitor 5. Note that the principle ofoperation differs between the examples illustrated in FIGS. 1 to 6B andthe example illustrated in FIG. 7. In FIGS. 1 to 6B, an effect obtainedby current flowing primarily along the edge of the sheet conductor 2 isused. In contrast, in FIG. 7, resonance occurring in the sheet conductor2 is used. That is, in the case in which resonance is used, currentflows in a loop in which the slit 2S is at the center or the approximatecenter. With either principle of operation described in theabove-described examples, antenna characteristics may be improved byusing such sheet conductors. Thus, the principle of operation describedin the examples illustrated in FIGS. 1 to 6B or that described in theexample illustrated in FIG. 7 may be used.

In contrast, a resonant circuit is defined by the coil-shaped conductor31 of the feed coil 3 and the RFIC 13. The coil-shaped conductor 31 hasinductance and self-capacitance. The RFIC 13 is an external device andconnected to the feed coil 3. The RFIC 13 primarily has capacitance. Theresonant frequency of the resonant circuit that is defined by the sheetconductor 2 and the capacitor 5 is fixed to a frequency near theresonant frequency of the resonant circuit that includes the feed coil3. These resonant frequencies are fixed to a frequency near the carrierfrequency. Consequently, strong electromagnetic-field coupling occursbetween the feed coil 3 and the sheet conductor 2. As a result,electromagnetic field emissions may be highly efficiently provided fromthe sheet conductor 2.

The resonant frequency of the resonant circuit that includes the sheetconductor 2 may be determined in accordance with the capacitance of thecapacitor 5 and the length of the slit 2S. Moreover, even when acomponent or a metal housing in which a magnetic substance, such as amicrophone or a speaker, for example, is provided is approaching aregion other than the slit 2S in the sheet conductor 2, the resonantfrequency of the resonant circuit that includes the sheet conductor 2does not significantly change. Thus, the antenna characteristics of suchan antenna device are not affected by an environment in which theantenna device is installed, and consequently, stable antennacharacteristics are obtained.

For example, in the case in which a carrier signal in the 13.56 MHz bandis used to perform communication, the resonant frequency of the resonantcircuit that includes the feed coil 3 (the resonant frequency of theresonant circuit that is defined by the feed coil 3 and the RFIC 13) ispreferably set to about 13.56 MHz and the resonant frequency of theresonant circuit that includes the sheet conductor 2 is preferably setto about 13.8 MHz. By placing the resonant circuit that includes thefeed coil 3 and the resonant circuit that includes the sheet conductor 2close to each other, the resonant frequency of the resonant circuit thatincludes the feed coil 3 becomes about 13.1 MHz and the resonantfrequency of the resonant circuit that includes the sheet conductor 2becomes about 14.2 MHz, for example. That is, when coupling occursbetween the two resonant circuits, two resonant frequencies occur in acoupling mode and gain will be obtained in the frequency bands of theresonant frequencies in the coupling mode. That is, the frequency bandin which communication may be performed is widened by setting theresonant frequency of the resonant circuit that includes the sheetconductor 2 to be different from the resonant frequency of the resonantcircuit that includes the feed coil 3.

FIG. 9 is a perspective view of another antenna device according to thefourth preferred embodiment. The structure of the sheet conductor 2 andthat of the feed coil 3 are preferably the same or substantially thesame as those illustrated in FIG. 4. In an example illustrated in FIG.9, the capacitor 5 is mounted on a board 1 and the capacitor 5 isconnected to the sheet conductor 2 via spring pins 6 so as to straddlethe slit 2S. The inductance of an inductor that contributes to theresonance of the resonant circuit that includes the sheet conductor 2 isdetermined by the electrical length of current that flows along the edgeof the slit 2S, the edge of the opening 2A, and the spring pins 6. Withthis structure, there is no need to provide a capacitor on the sheetconductor 2 and, thus, this structure has an advantage in that it iseasy to manufacture such an antenna device. Note that, in FIG. 9, thefeed coil 3 may be arranged on the sheet conductor 2 or may be arrangedon the board 1 similarly to the capacitor 5. In the case in which thefeed coil 3 and the capacitor 5 are mounted on the board 1, the feedcoil 3 and the capacitor 5 may be integrated into a single device byusing a multilayer board or other suitable structure.

Fifth Preferred Embodiment

FIG. 10 is a perspective view of an antenna device according to a fifthpreferred embodiment of the present invention. The slit 2S and theopening 2A are provided in the sheet conductor 2. The slit 2S preferablyhas a substantial meandering-line shape. That is, the sheet conductor 2is preferably cut to have a substantial comb-shape therein. Thus, acapacitor is provided at the slit 2S and the capacitance of the slit 2Sincreases. In contrast, an inductor is provided at the edge of theopening 2A. A resonant circuit is defined by the inductor provided atthe edge of the opening 2A and the capacitor provided at the slit 2S.With this structure, a chip capacitor as an additional component isunnecessary. The slit 2S that has a substantial meandering-line shapemay preferably be formed by a patterning method including etching, forexample, and thus, a necessary capacitance may be obtained with highaccuracy.

Note that the feed coil 3 is preferably arranged such that one of thecoil openings of the feed coil 3 faces a portion of the edge of theopening 2A. Thus, strong magnetic-field coupling occurs between the feedcoil 3 and the opening 2A.

FIG. 11A is a perspective view of the sheet conductor 2 included inanother antenna device according to the fifth preferred embodiment andFIG. 11B is a front view of the other antenna device. In this example,the sheet conductor 2 is provided on the top surface of the board 1,which has a flexible sheet-shaped structure, and a capacitor formationelectrode 7 is provided on the bottom surface of the board 1. Thecapacitor formation electrode 7 is preferably arranged at a positionthat faces the conductor portions on both sides of the slit 2S of thesheet conductor 2. With this structure, a chip capacitor as anadditional component is unnecessary.

Sixth Preferred Embodiment

FIGS. 12A and 12B are perspective views of antenna devices according toa sixth preferred embodiment of the present invention. In both examplesillustrated in FIGS. 12A and 12B, the two sheet conductors 2 a and 2 bare included. The slit 2S is provided between the sheet conductors 2 aand 2 b. A capacitor 5 a is connected to the sheet conductors 2 a and 2b at near one of the ends of the slit 2S and a capacitor 5 b isconnected to the sheet conductors 2 a and 2 b at near the other end ofthe slit 2S. The inductance of an inductor that contributes todetermination of a resonant frequency of a resonant circuit thatincludes the sheet conductors 2 a and 2 b is determined by the length ofthe edge of the slit 2S. A resonant circuit is defined by the inductorand the two capacitors 5 a and 5 b. The remainder of the antenna deviceis preferably the same or substantially the same as that described inthe third preferred embodiment with reference to FIG. 6.

As described above, even with the structure in which a slit is providedbetween a plurality of sheet conductors, the resonant frequency of aresonant circuit that includes sheet conductors may be determined.

Note that when the sheet conductors 2 a and 2 b are at the samepotential in a DC manner, the sheet conductors 2 a and 2 b may be usedas shield conductors.

Seventh Preferred Embodiment

FIG. 13 is a plan view illustrating an internal structure of a wirelesscommunication device that includes an antenna device according to aseventh preferred embodiment. This wireless communication devicepreferably is a communication terminal device, a typical example ofwhich is a smartphone. Circuit boards 71 and 81, a battery pack 83, andother components are included in a housing 91. An RFIC 60, whichincludes a communication circuit, the feed coil 3, the capacitor 5, andother components are mounted on the circuit board 71. An UHF-bandantenna 72, a camera module 76, and other components are also mounted onthe circuit board 71. Moreover, an UHF-band antenna 82 and othercomponents are mounted on the circuit board 81. The circuit boards 71and 81 are connected to each other via a coaxial cable 84.

A ground conductor provided on the circuit board 71 functions as a sheetconductor. The slit 2S and the opening 2A are provided in the groundconductor. The capacitor 5 is mounted at an end, which is positionednear the edge of the sheet conductor 2, of the slit 2S so as to straddlethe slit 2S. Moreover, the feed coil 3 is mounted in the opening 2A. Thefeed coil 3 is arranged such that the feed coil 3 is close to a portionof the edge of the opening 2A and one of the coil openings of the feedcoil 3 faces the portion of the edge of the opening 2A. Thus, strongcoupling occurs for the feed coil 3 through a magnetic field generatedfor the opening 2A.

In an example illustrated in FIG. 13, there is no need to provide adedicated component as a sheet conductor and the number of requiredcomponents is reduced. Moreover, communication may be performed withboth sides of the housing of the wireless communication device.Moreover, when the capacitance of the capacitor 5 is set to be a largevalue with which the capacitor 5 functions as a bypass capacitor in theUHF band, a high-frequency current from an UHF-band antenna does notflow near the feed coil 3. Thus, the characteristics of an UHF-bandantenna are not deteriorated under the influence of (the material of)the feed coil 3.

FIG. 14 is a perspective view of the feed coil 3, which is modularized,according to the seventh preferred embodiment. The feed coil 3 uses, asan element assembly, a multilayer body formed by stacking a ceramiclayer and resin layers. The multilayer body is preferably made of amagnetic layer 11 and non-magnetic (dielectric) layers 12, thenon-magnetic layers 12 sandwiching the magnetic layer 11. A firstcoil-shaped conductor 21 is provided around the magnetic layer 11. Asecond coil-shaped conductor is provided inside the magnetic layer 11.The RFIC 60 and a chip component 61, such as a chip inductor or a chipcapacitor, for example, are mounted on the top surface of the multilayerbody. A capacitor used to set the resonant frequency is defined by anelectrode pattern on a dielectric layer 12. In this manner, componentsincluded in a feeder circuit may be modularized.

Eighth Preferred Embodiment

FIG. 15 includes diagrams illustrating an internal structure of awireless communication device that includes an antenna device accordingto an eighth preferred embodiment of the present invention. FIG. 15includes plan views that separately show a state of the inside of anupper housing 91 and a state of the inside of a lower housing 92. Inthis example, the lower housing 92 is preferably made of resin and thesheet conductor 2, which is preferably a metal film, is provided in thelower housing 92. The sheet conductor 2 may be provided such that asheet conductor is attached to a flexible board or may be drawn on theinner-side surface of the lower housing 92 by laser direct structuring(LDS). Slit sections 2Sa and 2Sb and the opening 2A are provided in thesheet conductor 2. A section of the housing corresponding to the opening2A also includes an opening. The camera module 76 is preferably arrangedsuch that a lens of the camera module 76 is optically exposed from theopening of the housing.

FIG. 15 illustrates an example in which the feed coil 3 is preferablyarranged such that one of the coil openings of the feed coil 3 faces theclosed end (an end that is far from the opening 2A) of the slit section2Sb and the direction of the axis of the feed coil 3 is perpendicular orsubstantially perpendicular to the width direction of the closed end ofthe slit portion 2Sb. With this structure, coupling occurs for the feedcoil 3 through a magnetic field generated by the current that flowsalong the closed end of the slit section 2Sb. That is, coupling occursbetween the feed coil 3 and the sheet conductor 2. The remainder of thestructure in the upper housing 91 is preferably the same orsubstantially the same as that illustrated in FIG. 13.

Ninth Preferred Embodiment

FIG. 16A is a perspective view of an antenna device according to a ninthpreferred embodiment of the present invention and FIG. 16B is a frontview of the antenna device. In this example, the antenna device includesthe two sheet conductors 2 a and 2 b. The sheet conductor 2 a is, forexample, a ground conductor provided on a circuit board. The sheetconductor 2 b is a metal housing portion that is a portion of thehousing of a communication terminal. The sheet conductor 2 b includestwo wall portions, which are preferably substantially sheet-shaped, anda main surface portion provided between the wall portions. The sheetconductor 2 a is a ground conductor and is provided on a front layer oran inner layer of the circuit board. The feed coil 3 is mounted as achip-type component on the front layer of the circuit board. The circuitboard is a printed wiring board. Although not illustrated, variouscomponents, such as a cellular RF circuit and a driving circuit for adisplay device, for example, may preferably mounted on the circuitboard.

The slits 2Sa and 2Sb are provided between the sheet conductors 2 a and2 b. That is, a side of the sheet conductor 2 a and a side of the sheetconductor 2 b face each other via the slit 2Sa, and another side of thesheet conductor 2 a and another side of the sheet conductor 2 b faceeach other via the slit 2Sb. More specifically, the slit 2Sa is providedbetween one of the wall portions of the sheet conductor 2 b and thesheet conductor 2 a, and the slit 2Sb is provided between the other oneof the wall portions of the sheet conductor 2 b and the sheet conductor2 a. The sheet conductor 2 a and each of the wall portions of the sheetconductor 2 b are preferably arranged such that a directionperpendicular or substantially perpendicular to the sheet conductor 2 ais perpendicular or substantially perpendicular to a directionperpendicular or substantially perpendicular to the wall portion.

The metal housing portion is preferably made of conductive material, forexamples, magnesium, aluminum, and/or carbon fiber. The sheet conductor2 a is also preferably made of conductive material. Other than theground conductor of the printed wiring board, various metallic bodies,such as a metal chassis, a shield case, or a metal cover of a batterypack arranged in the communication terminal may preferably be used asthe sheet conductor 2 a.

The feed coil 3 is arranged at a position closer to the sheet conductor2 a than to the sheet conductor 2 b. That is, the feed coil 3 ispreferably arranged so as to be close to the sheet conductor 2 a suchthat the direction of the axis of the feed coil 3 is parallel orsubstantially parallel to the directions in which the sheet conductor 2a extends. In this manner, in the case in which spaces defined by aplurality of sheet conductors that are adjacent to each other are usedas slits, it a feed coil is preferably arranged such that the directionof the axis of the feed coil differs from a direction perpendicular orsubstantially perpendicular to one of the plurality of sheet conductors,the sheet conductor being closest to the feed coil.

In FIG. 16A, arrows drawn with a broken line represent the flow ofcurrent that flows along the edge of the sheet conductor 2 a and theflow of current that flows along the edge of the sheet conductor 2 b.Moreover, in FIG. 16B, arrows represent magnetic flux that passesthrough the slits 2Sa and 2Sb. For example, by placing the sheetconductor 2 b close to an antenna coil with which communication isperformed, an induced current is generated in the sheet conductor 2 band the induced current flows primarily along the edge of the sheetconductor 2 b due to the cut-edge effect. Then, a current is induced inthe sheet conductor 2 a that is adjacent to the sheet conductor 2 b viathe slits 2Sa and 2Sb. This current flows primarily along the edge ofthe sheet conductor 2 a due to the cut-edge effect. Furthermore,coupling between the feed coil 3 and the sheet conductors 2 a and 2 boccurs through a magnetic field that passes the slit 2Sa.

Note that when the sheet conductors 2 a and 2 b are at the samepotential in a DC manner, the sheet conductors 2 a and 2 b maypreferably be used as shield conductors. That is, the sheet conductors 2a and 2 b may be electrically independent from each other or may beconnected to each other via a power-supply pin, for example.

In this manner, two sheet conductors are not in one plane and are indifferent planes, and the slits 2Sa and 2Sb may be provided between thesheet conductors, which are in different planes. Similar effects andadvantages may be obtained. In particular, according to the ninthpreferred embodiment, there is no need to provide, in the metal housingportion, a slit or an opening used for coupling that occurs for the feedcoil 3. Thus, the strength of the metal housing portion is not greatlyreduced and a degree of flexibility in the design of the housing isimproved.

Note that a state in which the feed coil 3 is arranged is not limited tothose illustrated in FIGS. 16A and 16B. FIG. 17 is a front view of anantenna device that illustrates another exemplary state in which thefeed coil 3 is arranged. As illustrated in FIG. 17, sheet conductors 2 aare ground conductors and are provided on front layers (or on an innerlayer) of an insulating board 2 c. The feed coil 3 is mounted on an areaof the insulating board 2 c, the area being an area in which a sheetconductor 2 a is not provided. The feed coil 3 may preferably bearranged such that the direction of the axis of the feed coil 3 isperpendicular or substantially perpendicular to the directions in whichthe insulating board 2 c extends and a portion of one of the coilopenings of the feed coil 3 is at a position that overlaps the slit 2Sa.Even in this case, coupling between the feed coil 3 and the sheetconductors 2 a and 2 b occurs through a magnetic field that passes theslit 2Sa.

Tenth Preferred Embodiment

FIG. 18A is a perspective view of an antenna device according to a tenthpreferred embodiment of the present invention and FIG. 18B is a frontview of the antenna device. FIG. 19 is a side view of the antennadevice. In this example, similarly to the ninth preferred embodiment,two sheet conductors 2 a and 2 b are included. This example differs fromthe ninth preferred embodiment in that connection units 2 b 1, 2 b 2, 2b 3, and 2 b 4 are provided so as to straddle the slits 2Sa and 2Sb andthe slits 2Sa and 2Sb are partially connected to each other.

The sheet conductor 2 a and electrode patterns 2 a 1 and 2 a 2 areprovided on a circuit board 2 c. The electrode patterns 2 a 1 and 2 a 2are not electrically connected to the sheet conductor 2 a. Similarly tothe ninth preferred embodiment, the sheet conductor 2 a is, for example,a ground conductor provided on the circuit board 2 c and the sheetconductor 2 b is a portion of the metal housing. The slits 2Sa and 2Sbare provided between the circuit board 2 c and the sheet conductor 2 b.Note that, other than the ground conductor, various metallic bodies,such as a metal chassis, a shield case, or a metal cover of a batterypack, may preferably be used as the sheet conductor 2 a.

The sheet conductor 2 b is connected to the circuit board 2 c by theconnection units 2 b 1 and 2 b 2 such that the sheet conductor 2 b iselectrically connected to the electrode patterns 2 a 1 and 2 a 2 at bothends of the slit 2Sa in the longitudinal direction. As described above,the electrode patterns 2 a 1 and 2 a 2 are not electrically connected tothe sheet conductor 2 a. Thus, the sheet conductor 2 b is notelectrically connected to the sheet conductor 2 a on the side at whichthe slit 2Sa is provided.

Moreover, the sheet conductor 2 b is connected to the circuit board 2 cby the connection units 2 b 3 and 2 b 4 such that the sheet conductor 2b is electrically connected to the sheet conductor 2 a at both ends ofthe slit 2Sb in the longitudinal direction. Note that the sheetconductor 2 b may be connected to the circuit board 2 c such that theslit 2Sb is not provided.

Note that the connection units 2 b 1, 2 b 2, 2 b 3, and 2 b 4 maypreferably be metal screws, solder, or conductive paste, for example.Moreover, the sheet conductor 2 b may have a structure in which thesheet conductor 2 b is fitted into the sheet conductor 2 a.

Similarly to the ninth preferred embodiment, the feed coil 3 is mountedon the circuit board 2 c on the side at which the slit 2Sa is provided.

A capacitor 5 c is provided on the circuit board 2 c. The capacitor 5 cconnects the electrode pattern 2 a 1 with the sheet conductor 2 a. Thesheet conductors 2 a and 2 b are electrically connected with each otherby the connection units 2 b 1 and 2 b 3 and the capacitor 5 c. Asillustrated in FIG. 18B, an opening A provided by the sheet conductors 2a and 2 b functions as an inductor. An LC circuit is defined by theinductor and the capacitor 5 c. The capacitance of the capacitor 5 c isset to a capacitance at which resonance occurs for the LC circuit in thecarrier-frequency band for a communication signal or near thecarrier-frequency band.

In FIGS. 18A and 18B, magnetic flux φ2 represents magnetic flux thatpasses through the feed coil 3 and the slit 2Sa. In this manner, acurrent is induced in the sheet conductor 2 a by magnetic flux passingthrough the slit 2Sa. As a result, current flows in the sheet conductors2 a and 2 b along the opening A. That is, a loop is provided around theopening A and current flows in the loop with its center at the openingA. Consequently, magnetic flux enters and leaves the opening A and theopening A functions as a radiation unit in the antenna device asindicated by an arrow in FIG. 19.

Note that, as indicated by arrows drawn with a broken line, an eddycurrent flows in a portion of the sheet conductor 2 a, the portion beinglocated outside the opening A, so as to cancel magnetic flux emittedfrom the opening A. Thus, a magnetic field emitted from the opening Atends to be emitted such that the magnetic field is bent toward the sideat which the sheet conductor 2 b is provided.

In the tenth preferred embodiment, a structure in which the length ofthe sheet conductor 2 b in the longitudinal direction is shorter thanthat of the sheet conductor 2 a is preferable. With this structure,magnetic flux is emitted from the opening A toward the side at which thesheet conductor 2 b is provided. Communication may be more efficientlyperformed by orienting the sheet conductor 2 b toward an antenna withwhich communication is performed. Moreover, the capacitor 5 c may be avariable capacitor and the resonant frequency may be variable.

Eleventh Preferred Embodiment

FIG. 20 is a perspective view of an antenna device according to aneleventh preferred embodiment of the present invention. In this example,electrode patterns 2 a 3 and 2 a 4, which are not electrically connectedto the sheet conductor 2 a, are further provided on the circuit board 2c. The electrode patterns 2 a 2 and 2 a 3 are electrically connected tothe sheet conductor 2 a by inductors 8 a and 8 b, respectively.Moreover, the electrode pattern 2 a 4 is electrically connected to thesheet conductor 2 a by a capacitor 5 d.

With this structure, an inductor is provided at the edge of the slit2Sa. An LC circuit is defined by the inductor and the capacitor 5 c. Byusing the inductor 8 a, the inductance of the LC circuit is easily setto an inductance with which resonance occurs for the LC circuit in thecarrier-frequency band for a communication signal or near thecarrier-frequency band, in contrast to a case in which only the inductorprovided at the edge of the slit 2Sa is used. Similarly, a current isinduced by magnetic flux that passes through the slit 2Sb, even at theedge of the slit 2Sb in the direction indicated by arrows. That is,magnetic flux is emitted even from the slit 2Sb.

Twelfth Preferred Embodiment

FIG. 21 is an exploded perspective view of a feed coil used in anantenna device according to a twelfth preferred embodiment of thepresent invention. A feed coil 3 c according to the twelfth preferredembodiment includes an inductance value and a capacitance value.Specifically, as illustrated in FIG. 21, the feed coil 3 c includes anon-magnetic layer 311 a, a magnetic layer 311 b, and a plurality ofmagnetic layers 312. The feed coil 3 c has a structure in which theplurality of magnetic layers 312 are sandwiched by the non-magneticlayer 311 a and the magnetic layer 311 b. An in-plane conductor 321 a isprovided on the non-magnetic layer 311 a and an in-plane conductor 321 bis provided on the magnetic layer 311 b. The in-plane conductors 321 aand 321 b are a portion of a coil pattern. Although not illustrated,side-surface vias are provided on the side surfaces of the magneticlayers 312. The side-surface vias are used to connect the in-planeconductor 321 a of the non-magnetic layer 311 a with the in-planeconductor 321 b of the magnetic layer 311 b.

Moreover, plane conductor patterns 312 a and 312 b are provided on twomagnetic layers 312 positioned near the axis of the feed coil 3 c fromamong the plurality of magnetic layers 312. The plane conductor patterns312 a and 312 b face each other in the stacking direction and define acapacitor. The magnetic field generated from the coil pattern isstrongest near the in-plane conductors 321 a and 321 b and becomesweaker towards the axis of the feed coil 3 c. Thus, when a capacitor isprovided near the axis of the feed coil 3 c, the capacitor does notgreatly affect the antenna characteristics.

The non-magnetic layer 311 a is stacked on a non-magnetic layer 313 onwhich input-output terminals 331 a, 331 b, 331 c, and 331 d areprovided. Note that the input-output terminals 331 a, 331 b, 331 c, and331 d may be provided on a surface of the non-magnetic layer 311 aopposite the surface on which the in-plane conductor 321 a is provided.Alternatively, the in-plane conductor 321 a may be provided on thebottom surface of the non-magnetic layer 311 a and the non-magneticlayer 311 a may be a magnetic layer.

The input-output terminal 331 a is connected to an end of the coilpattern and the input-output terminal 331 c is connected to the otherend of the coil pattern. That is, the input-output terminals 331 a and331 c are input-output terminals of the coil of the feed coil 3 c.Moreover, the plane conductor pattern 312 b is connected to theinput-output terminal 331 b, and the plane conductor pattern 312 a isconnected to the input-output terminal 331 d. That is, the input-outputterminals 331 b and 331 d are preferably input-output terminals of thecapacitor.

FIG. 22 is a diagram illustrating a portion of a board on which a feedcoil according to the twelfth preferred embodiment is mounted. Thecircuit board 2 c and the sheet conductor 2 a provided on the circuitboard 2 c illustrated in FIG. 22 are preferably the same as or similarto those in the tenth and eleventh preferred embodiments. In FIG. 22,electrode patterns used for terminals (hereinafter referred to as“terminal-use electrode patterns”) are denoted by 101 a, 101 b, and 101c. The terminal-use electrode patterns 101 a, 101 b, and 101 c are notelectrically connected to the sheet conductor 2 a. The feed coil 3 c ispreferably arranged such that the input-output terminals 331 a, 331 b,331 c, and 331 d are electrically connected to the terminal-useelectrode pattern 101 c, the sheet conductor 2 a, the terminal-useelectrode pattern 101 b, and the terminal-use electrode pattern 101 a,respectively. An RFIC 15 is connected to the terminal-use electrodepatterns 101 b and 101 c. The sheet conductor 2 b, which has alreadybeen described in the tenth and eleventh preferred embodiments, isconnected to the terminal-use electrode pattern 101 b by the connectionunit 2 b 1 (see FIG. 18A).

With this structure, the feed coil 3 c includes an inductance value anda capacitance value. Thus, the capacitor 5 c is not necessary as anadditional component, which has already been described in the tenth andeleventh preferred embodiments. As a result, a capacitor may be builtinto without enlarging the size of an antenna, and consequently, spacesavings on the circuit board is achieved.

Note that a capacitor provided in the feed coil 3 c may be arranged inthe stacking direction, or in a direction perpendicular or substantiallyperpendicular to the stacking direction, that is, in a direction alongthe surface of each layer. Moreover, the feed coil 3 c may include aplurality of capacitors.

A modified example of the feed coil according to the twelfth preferredembodiment will be described below.

FIG. 23 is an exploded perspective view of a feed coil of anotherexample. A feed coil 3 d in this example has a structure in which themagnetic layers 312 on which the plane conductor patterns 312 a and 312b are provided are stacked under the non-magnetic layer 311 a andmagnetic layer 311 b on which the in-plane conductors 321 a and 321 bare provided, the in-plane conductors 321 a and 321 b being a portion ofa coil pattern. That is, the distance from the sheet conductor 2 a tothe coil of the feed coil 3 d is ensured by provided a capacitor betweenthe coil of the feed coil 3 d and the sheet conductor 2 a. Thus, aninfluence caused by the sheet conductor 2 a is reduced.

Note that the non-magnetic layer 311 a may be a magnetic layer.Moreover, a plurality of magnetic layers 312 arranged above the in-planeconductor 321 a in FIG. 23 may be replaced with non-magnetic layers.Note that, for each of the layers, whether the layer is a magnetic layeror a non-magnetic layer may be selected as necessary in accordance witha purpose.

FIG. 24 is an exploded perspective view of a feed coil of anotherexample of a preferred embodiment of the present invention. Similarly tothe example illustrated in FIG. 23, a feed coil 3 e in this example hasa structure in which a capacitor is defined by the plane conductorpatterns 312 a and 312 b between the coil of the feed coil 3 e and thesheet conductor 2 a. Furthermore, an electrode pattern 312 c, whichsubstantially has a meandering shape, is provided on one of a pluralityof magnetic layers 312 sandwiched between the non-magnetic layer 311 aand the magnetic layer 311 b, on which the in-plane conductors 321 a and321 b are provided, the in-plane conductors 321 a and 321 b being aportion of a coil pattern. One end of the electrode pattern 312 c iselectrically connected to the plane conductor pattern 312 b, and theother end of the electrode pattern 312 c is electrically connected tothe input-output terminal 331 b by side-surface vias, not illustrated.The plane conductor pattern 312 a is electrically connected to theinput-output terminal 331 d. Note that a plurality of magnetic layers312 and the magnetic layer 311 b may be non-magnetic layers and thenon-magnetic layer 311 a may be a magnetic layer.

As a result, an LC circuit that includes a capacitor defined by theplane conductor patterns 312 a and 312 b and an inductor defined by theelectrode pattern 312 c is connected between the input-output terminals331 b and 331 d, the capacitor and the inductor being connected inseries. The inductor defined by the electrode pattern 312 c may add aninductance value when an inductance value is insufficient due to theopening A, which has been described with reference to FIG. 18A, forexample. An LC circuit for which resonance occurs in thecarrier-frequency band for a communication signal or near thecarrier-frequency band is obtained.

Note that cases in which the antenna devices perform a receptionoperation have been described in the first to ninth preferredembodiments described above. However, coupling similarly occurs even incases in which the antenna devices function as transmission antennas inaccordance with a law of reciprocity for antennas. That is, a currentinduced by a magnetic field generated by a feed coil flows in a sheetconductor of an antenna device, so as to generate a magnetic field.Coupling occurs with another antenna, with which communication isperformed, through the magnetic field.

Moreover, the antenna devices according to the preferred embodiments ofthe invention described above preferably include a sheet conductor as aradiator, and thus, communication may be performed with another antenna,with which communication is performed, by orienting either of the mainsurfaces of the sheet conductor toward the other antenna.

Moreover, the sheet conductor may be arranged between the feed coil andthe other antenna, or the feed coil may be arranged between the sheetconductor and the other antenna.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. An antenna device comprising: a feed coilincluding a coil-shaped conductor; and a sheet conductor having a sheetshape; wherein the sheet conductor has an area larger than an area ofthe feed coil; a slit that extends from a portion of an edge of thesheet conductor toward an inner side of the sheet conductor is providedin the sheet conductor, or an opening and the slit are provided in thesheet conductor, the opening being connected to the slit; the feed coilis arranged such that a direction of an axis around which thecoil-shaped conductor is disposed differs from a direction perpendicularor substantially perpendicular to the sheet conductor; and the feed coilis arranged such that a coil opening at one end of the coil-shapedconductor is adjacent to the slit, or a portion of an edge of theopening and the coil opening faces the slit or the portion of the edgeof the opening.
 2. An antenna device comprising: a feed coil thatincludes a coil-shaped conductor; and a plurality of sheet conductors;wherein a slit is provided or an opening and the slit are providedbetween adjacent sheet conductors of the plurality of sheet conductors,the opening being connected to the slit; a total area of the pluralityof sheet conductors is larger than an area of the feed coil; the feedcoil is arranged such that a direction of an axis around which thecoil-shaped conductor is disposed differs from at least a directionperpendicular or substantially perpendicular to one of the plurality ofsheet conductors arranged closest to the feed coil; and the feed coil isarranged such that a coil opening at one end of the coil-shapedconductor is close to the slit, or a portion of an edge of the openingand the coil opening faces the slit or the portion of the edge of theopening.
 3. The antenna device according to claim 2, wherein theplurality of sheet conductors are connected to each other in a directcurrent manner and are at the same potential.
 4. The antenna deviceaccording to claim 2, wherein the plurality of sheet conductors includea first conductor surface and a second conductor surface that face eachother; the antenna device further comprises: a first connection unitelectrically and directly connecting the first conductor surface withthe second conductor surface; and a second connection unit connectingthe first conductor surface with the second conductor surface via afirst capacitor.
 5. The antenna device according to claim 4, wherein thefeed coil has a multilayer structure including a plurality of insulatorlayers on which a conductor that defines an inductor is provided and aplurality of insulator layers on which a conductor that defines acapacitor is provided are stacked; and the first capacitor is defined bythe capacitor included in the feed coil.
 6. The antenna device accordingto claim 1, wherein the slit includes at least one bend portion.
 7. Theantenna device according to claim 1, wherein the axis around which thecoil-shaped conductor is disposed is arranged so as to be perpendicularor substantially perpendicular to the direction in which the slitextends or to a portion of the edge of the opening.
 8. The antennadevice according to claim 1, wherein the sheet conductor includes aresonant circuit that is primarily defined by the slit or the edge ofthe opening; and a resonant frequency of the resonant circuit issubstantially the same as a resonant frequency of a circuit thatincludes the feed coil.
 9. The antenna device according to claim 1,wherein at least a portion of the sheet conductor is defined by a metalhousing.
 10. The antenna device according to claim 1, wherein at least aportion of the sheet conductor is defined by a ground conductor providedon a circuit board.
 11. A wireless communication device comprising: anantenna device; and a communication circuit connected to the antennadevice; wherein the antenna device includes a feed coil and a sheetconductor, the feed coil including a coil-shaped conductor; the sheetconductor has an area larger than an area of the feed coil; a slit thatextends from a portion of an edge of the sheet conductor toward an innerside of the sheet conductor is provided in the sheet conductor or anopening and the slit are provided in the sheet conductor, the openingbeing connected to the slit; the feed coil is arranged such that adirection of an axis around which the coil-shaped conductor is disposeddiffers from a direction perpendicular or substantially perpendicular tothe sheet conductor; and the feed coil is arranged such that a coilopening at one end of the coil-shaped conductor is close to the slit ora portion of an edge of the opening and the coil opening faces the slitor the portion of the edge of the opening.
 12. The wirelesscommunication device according to claim 11, wherein the slit includes atleast one bend portion.
 13. The wireless communication device accordingto claim 11, wherein the axis around which the coil-shaped conductor isdisposed is arranged so as to be perpendicular or substantiallyperpendicular to the direction in which the slit extends or to a portionof the edge of the opening.
 14. The wireless communication deviceaccording to claim 11, wherein the sheet conductor includes a resonantcircuit that is primarily defined by the slit or the edge of theopening; and a resonant frequency of the resonant circuit issubstantially the same as a resonant frequency of a circuit thatincludes the feed coil.
 15. The wireless communication device accordingto claim 11, wherein at least a portion of the sheet conductor isdefined by a metal housing.
 16. The wireless communication deviceaccording to claim 11, wherein at least a portion of the sheet conductoris defined by a ground conductor provided on a circuit board.
 17. Awireless communication device comprising: an antenna device; and acommunication circuit that is connected to the antenna device; whereinthe antenna device includes a feed coil and a plurality of sheetconductors, the feed coil including a coil-shaped conductor; a slit isprovided or an opening and the slit are provided between adjacent sheetconductors of the plurality of sheet conductors, the opening beingconnected to the slit; a total area of the plurality of sheet conductorsis larger than an area of the feed coil; the feed coil is arranged suchthat a direction of an axis around which the coil-shaped conductor isdisposed differs from at least a direction perpendicular orsubstantially perpendicular to one of the plurality of sheet conductorsclosest to the feed coil; and the feed coil is arranged such that a coilopening at one end of the coil-shaped conductor is close to the slit ora portion of an edge of the opening and the coil opening faces the slitor the portion of the edge of the opening.
 18. The wirelesscommunication device according to claim 17, wherein the plurality ofsheet conductors are connected to each other in a direct current mannerand are at the same potential.
 19. The wireless communication deviceaccording to claim 17, wherein the plurality of sheet conductors includea first conductor surface and a second conductor surface that face eachother; the antenna device further comprises: a first connection unitelectrically and directly connecting the first conductor surface withthe second conductor surface; and a second connection unit connectingthe first conductor surface with the second conductor surface via afirst capacitor.
 20. The wireless communication device according toclaim 19, wherein the feed coil has a multilayer structure including aplurality of insulator layers on which a conductor that defines aninductor is provided and a plurality of insulator layers on which aconductor that defines a capacitor is provided are stacked; and thefirst capacitor is defined by the capacitor included in the feed coil.